During the development of the first scientific part, catalytic alkane metathesis (CAM) has been evaluated as a suitable approach to upcycle hydrocarbons (polyolefins) at moderate temperatures. This process entails the use of a tandem catalyst which usually consists of a combination of two independent functions: one active in the alkane dehydrogenation reaction and other in the alkene metathesis process, which is usually based on Re2O7. In this context, a pincer-ligated iridium complex (dehydrogenation catalyst) has been combined with a rhenium-based (metathesis) catalyst, being the effect of immobilizing the Ir complex over different supports deeply investigated during the project. α-Al2O3 and SiO2 have been used as supports to immobilize the Ir complex along with TiO2 and three zeolites: mordenite and two ZSM-5 samples with different SiO2/Al2O3 molar ratio, respectively. FTIR spectroscopy has been used to confirm the complex grafting and to elucidate the anchoring site to the support. Additionally, the supports have been dehydroxylated at different conditions to evaluate its possible impact in both the complex grafting and the catalytic activity. All the catalysts have been evaluated in the cross-alkane metathesis of n-dodecane and n-octane, molecules acting as models of heavy (polyethylene) and light alkanes, respectively. To the best of our knowledge, this is the first time that both support nature effect and support dehydroxylation effect are systematically evaluated in the degradation of heavy alkanes through CAM with light alkanes over supported pincer-ligated iridium complexes. The optimized systems lead to a range of alkanes but also to light alkenes, one of the main objectives of the project. Moreover, it has been demonstrated that the product distribution depends not only on the support type but also on support dehydroxylation which open a new research line towards catalyst optimization for plastic upcycling.
On the other hand, the conversion of light alkenes to glycols involves two cascade reactions, the alkene epoxidation and the epoxide ring opening to form glycols. The work done within this part has involved the optimization of catalysts based on gold nanoparticles supported over titanium containing zeolites. Different synthetic methods have been explored along with different zeolite compositions, and methods for gold impregnation. The optimization of gold deposition has constituted an important scientific achievement. Preliminary results regarding light alkenes epoxidation have been very promising, leading to potential systems for the production of glycols in liquid media.
The last scientific part involved the optimization of catalysts and reaction conditions for the joint (ep)oxidation of light alkenes and HMF. Although the synthetized catalysts for alkenes epoxidation are potentially active in the HMF oxidation reaction over the same reaction conditions, this step was not investigated due to the premature end of the project. However, it will be part of future work.
The results have been disseminated in several ways although, unfortunately, all programed activities were not able to be undertaken due to the project end. The project results have been exposed during group meeting presentations and were sent in abstract format to the 15th European Congress on Catalysis (EuropaCat2023) and to the Spanish Conference on Catalysis (Secat2023) to be considered as part of the conferences program. Unfortunately, and due to the abrupt end of the project, the fellow was not able to participate in any of the conferences, programmed in June and August 2023. The project has been disseminated in a press release (
https://sevilla.abc.es/sevilla/sevi-investigacion-sevillana-apuesta-reciclar-202102200753_noticia.html(se abrirá en una nueva ventana)).
